1. Field of the Invention
The present invention is related generally to prosthetic orthopedic implants, particularly to joint components such as for use with knees, hips, shoulders, elbows, toes, fingers, wrists, ankles, spinal discs and the like. More specifically, the present invention relates to a method of making a non-modular prosthetic joint component having a polymer, ceramic, or metal bearing component bonded to a polymer, ceramic, or metallic substrate having at least one porous surface.
2. Description of the Related Art
Orthopedic implant devices known to those of skill in the art often comprise a backing component and bearing component attached thereto. Furthermore, it is often desirable for the metal backing component to comprise a porous structure or surface suitable for bone ingrowth after the prosthetic devise is implanted. For example, a typical prosthetic acetabular cup comprises a hemispherical metal backing having a porous convex exterior and a solid concave interior. A similarly hemispherical, but smaller, polymer bearing surface is inserted into to the concave interior of the backing. In another example, a typical tibial component for use during a knee arthroplasty comprises metal tibial plateau having a porous bone contacting surface and a polymer bearing component attached to an opposing surface.
In many instances, prosthetic joint devices are modular. A modular device comprises a backing component, generally comprising a biocompatible metal having a porous structure or surface, and a separate bearing surface component, generally comprising a polymer. For example, a modular acetabular cup comprises a metal backing component and a polymer bearing surface fixedly inserted therein. Such fixation may be achieved via any of one or more of a variety of known mechanical means, such as snap fitting the components, press fitting the components, threadably connecting the components, using a locking ring, etc.
Those of skill in the art recognized that these additional mechanical retaining means could be avoided by using non-modular (“monoblock”) joint components. Monoblock joint components comprise a metal backing such as a metal acetabular shell or a metal tibial plateau with the bearing surface integrally attached thereto. Unlike a modular component, the bearing surface of a monoblock is integral with the bearing component and need not be mechanically attached to the metal backing of an implant during an intraoperative step. There are several monoblock prosthetic devices presently available. These devices are generally produced by directly compression molding a thermoplastic polymer bearing component onto a backing component. However, this method of producing monoblock devices has disadvantages.
More recently, the bearing components of traditional monoblock prosthetic devices often comprise cross-linked ultra high molecular weight polyethylene (“UHMWPE”). Cross linking can be accomplished chemically, but it is usually accomplished via gamma or electron beam irradiation after the monoblock device is assembled. A problem with this process is that the metal component of the monoblock device can shield the bearing component from the electron beam radiation used to initiate cross linking, thereby making cross linking of the bearing component more difficult and time consuming or possibly having areas within the polymer remaining uncrosslinked.
Another problem with monoblock processes known in the art is that such processes do not accommodate using non moldable materials such as metals or ceramics for the bearing surface, as the same cannot be compression or injection molded onto a backing component.
Thus, a need exists for a method of making a monoblock orthopedic joint device, wherein the polymer component can be cross-linked separately from the backing component and subsequently connected to thereto to form a monoblock device.
A still further need exists for a method of making a monoblock orthopedic joint utilizing a metal, ceramic or other non-flowable material for the bearing surface.